Tabqa dam on the Euphrates River is only 40 kilometres from the city of Raqqa which is held by Daesh, making it a front line in the battle to capture the city.
The dam is now partly controlled by the Syrian Democratic Forces (SDF), an opposition coalition which has support from the US.
The fight against Daesh is thought to have caused some damage to the dam. However, the SDF announced on Monday that the structure had been examined by engineers and was intact.
TRT World's Abubakr al-Shamahi has more on the essential water source.